Regional differences in sympathetic activation in lean and obese normotensive individuals with obstructive sleep apnoea.

Objective: Obstructive sleep apnoea (OSA) is characterized by a marked sympathetic overdrive, as documented by the elevated sympathetic nerve firing rate detected in peripheral muscle nerves. No data are available, however, on the behaviour of sympathetic drive in vascular regional districts other than the muscle circulation.

Design And Methods: In 66 middle-aged normotensive individuals classified according to BMI, waist-to-hip ratio and apnoea-hypopnea index as lean individuals without (n = 20) or with (n = 14) OSA and as obese individuals without (n = 13) or with (n = 19) OSA, we measured blood pressure, heart rate, muscle sympathetic nerve activity (MSNA) and skin sympathetic nerve activity (SSNA), respectively, via microneurography. Measurements also included SSNA responses to an emotional stimulus.

Results: The four groups were matched for age, sex and blood pressure values. Both in lean and obese individuals, presence of OSA was accompanied by MSNA values significantly greater than those found in non-OSA individuals. In contrast, no significant difference was found in SSNA values between OSA and non-OSA patients both in the lean and in the obese groups. This was the case also for the SSNA responses to an emotional arousal.

Conclusion: These data provide the first evidence that in OSA, the adrenergic overdrive seen in the muscle circulation is not detected in cutaneous circulation and thus it cannot be regarded as a generalized phenomenon affecting the whole cardiovascular system. Further studies are needed to clarify whether in OSA, sympathetic drive of other vascular districts, such as the coronary, renal or cerebral circulation, is activated or normal.